The present invention relates, in general, to a clamping unit with double crank drive.
Nothing in the following discussion of the state of the art is to be construed as an admission of prior art.
Clamping units are typically used for presses or injection molding machines. In general, injection molding machines have two mold halves for formation of a cavity which normally are held together through application of a great clamping pressure in order to be able to inject a plasticized melt into the cavity without escape. For this purpose, the molding tools are normally arranged on two platens of a clamping unit which can be moved to and away from one another. When the mold is closed, a plastic melt is introduced into the cavity for formation of a plastic product. When the mold is open, the thus-produced plastic product can then be removed after undergoing curing.
Clamping units can come in different configurations, such as a 3-platen clamping unit or a 2-platen clamping unit. A 2-platen clamping unit normally includes a fixed platen and a moving platen which are connected together via a pulling means. By means of such a pulling means, e.g. tie rods, the two platens can be moved in relation to one another and a clamping force can be applied. 3-platen clamping units normally include a fixed platen as well as a support platen. A moving platen is arranged between the fixed platen and the support platen and movable back and forth by a drive in relation to the fixed platen. The drive is normally arranged between the moving platen and the support platen. Known drive options include hydraulic clamping devices, such as hydraulic pistons or toggle systems, which can be hydraulically or electrically operated in many ways.
In toggle or connecting rod systems, the maximum stroke between the moving platen and the fixed platen is predefined by the toggle construction so that the distance between the support platen, on one hand, and the moving platen, on the other hand, can vary only within a defined distance range. Moreover, the clamping force can oftentimes be applied only in an extended disposition or dead center disposition.
The manufacture of different parts between the fixed platen and the moving platen requires different molds, in particular molds of different thickness, so that there is a general need for providing a toggle or connecting rod construction also with an adjustment mechanism to conform to a mold—either for the fixed platen or for the combination of moving platen, support platen and drive. This adjustment not only enables to match the distance between the fixed platen and the moving platen to the different mold thicknesses but also allows execution of a service or maintenance stroke. Numerous constructive solutions are known for this type of adjustment.
It would therefore be desirable and advantageous to provide an improved clamping unit to obviate prior art shortcomings and to be simple and robust in structure and cost-efficient to implement.